Satellite-based positioning systems such as Global Positioning System (GPS) are commonly integrated into automobiles to offer drivers navigation assistance. The assistance a GPS-guided navigation system can offer, however, depends upon successful receipt of GPS signals. In general, successful receipt of GPS signals depends upon line-of-sight contact with a plurality (three or more) of GPS satellites. Tall buildings often surround roads in urban areas creating artificial canyons that block successful reception. In addition, a driver may have entered an enclosed area such as a tunnel or parking garage that also prevents successful reception. Despite the lack of good reception, drivers continue to need navigation updates during these periods.
To provide navigation updates in the absence of GPS signal reception, a variety of dead reckoning enhancements have been offered as adjuncts to GPS navigation systems. Navigation using dead reckoning involves calculating a current position based upon the heading and distance from a previously known position. Dead reckoning has been used since ancient times in nautical applications prior to the development of celestial navigation. Sailors would use estimates of their speed and heading over a period of time to determine the relative change in position with regard to a previously-known position (such as a port) and thus deduce their current location.
In more modern applications such as automotive navigations systems, a dead reckoning system may get its necessary velocity measurements through a coupling to the car's odometer. However, such coupling involves considerable expense, particularly in an after-market application. Thus, dead reckoning systems have been developed that use accelerometers to provide velocity estimates from the integration of the acceleration. A problem remains, however, because the accelerometers must be precisely arranged with respect to the car to provide an accurate velocity estimate, thereby requiring an expensive and time-consuming installation.
Accordingly, there is a need in the art for improved dead reckoning systems that address these problems in the prior art.